This invention relates to wireless communication systems and, more particularly, to the establishment of system resource parameters as a function of user application requirements.
Wireless communication systems allow the transmission of information signals between a mobile user and a fixed based station. The base station will typically be interconnected with one or more landline communications networks. Both analog (first generation) and digital (second/third generation) systems have been developed to transmit information signals over communication channels linking the mobile user with landline networks. Digital methods tend to afford several advantages over analog systems, including improved immunity to channel noise and interference, increased capacity, and encryption for secure communications.
First generation wireless systems were primarily directed to voice communication, but the digital technology of second and third-generation systems provides support for both voice and data applications. Several modulation/coding arrangements have been developed, such as frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA), to increase the number of users that can access a wireless network. CDMA systems are more immune to multi-path distortion and co-channel interference than FDMA and TDMA systems and reduce the burden of frequency/channel planning that is common with FDMA and TDMA systems.
The base stations of a wireless network manage a variety of resources in the establishment of communications links with their associated mobile users. Among those resources are output power and data rate. Output power and data rate are proportionally relatedxe2x80x94the output power necessary to establish or maintain a link with a user increasing as the data rate increases. This increase in output power with increasing data rate is required to maintain the output energy per bit at a constant level. In the management of power output, a base station must balance the transmission needs of its users, individually and collectively, against inter-channel interference among the served mobile users, as well as constraints in respect to total output power for the base station.
Thus, upon a request for entry to the wireless network by a user, the base station must evaluate the user""s data rate and power demands against the current user environment and power demands. As the user environment approaches the total system capacity, the base station may delay the entry of a user onto the system to prevent overloading the output power capability of the base station.
In the prior art, allocation of power and system resources is typically based on channel conditions only. While the network is generally aware of application requirements, a conventional transmission network does not address channel conditions in the establishment of application layer operation. Typically, the physical layer of the data channel is optimized based on operating parameters relating to the physical channel only and the application layer is optimized based only on the application layer Quality of Service (QoS) requirements.
Moreover, in a communications system utilizing power control, the allocation of the available RF power is usually dictated by a required Frame Error Rate (FER), with the power control system having a feedback mechanism for adjusting power to maintain the required FER under varying channel conditions. Thus, for a given required FER, the output power will vary depending on the difference between the required FER and the FER experienced due to the channel. The instantaneous Eb/Io ratio (essentially, the digital signal-to-noise ratio) for the channel is controlled by the excursion around that set point in the inner loop of the power control system. Once a target FER is set, the power control system operates to dynamically allocate the RF power to overcome channel fades and interference in order to maintain the experienced FER within a tolerable deviation from the required FER.
With the current CDMA standard (IS-95A and B), the FER is a fixed system parameter set by an operator. For voice calls, FERs are usually set between 1% and 2% to meet a required Merit of Service (MoS) parameter. However, no MoS-like criteria exists for data applications.
Thus, there is a need to provide an efficient FER selection criteria for data applications and to provide a linkage between the application layer and the physical layer for a channel in respect to channel resource allocation.
A method is provided for intelligent utilization of the power and system resources in a wireless communication system through a multiple layer optimization. In particular, the invention provides dynamic interaction between the different protocol layers in the wireless system by intelligent mapping of application layer QoS requirements down to physical layer system operating parameters The method will seamlessly control the operating parameters in each individual layer adaptive to different radio link conditions and resource availability.
The methodology of the invention operates to map a set of data points relating to performance characteristics associated with the application layer to a corresponding set of data points relating to physical layer performance characteristics, and through such mapping, to determine an optimum resource allocation in respect to the application requirements and channel conditions. In a preferred embodiment of the invention, the performance characteristics are established in terms of frame error rate and data rate.
In support of the method of the invention, performance characteristics for the application and the channel are determined and stored in the form of a set of tables or corresponding curves (or mathematical equivalents thereof). A required performance parameter for the application under consideration (e.g., data throughput) is then determined and tested against the predetermined application performance criteria to find points of intersection with curves representing potential data rates for transmission through the channel. Data points representing such points of intersection are then mapped to corresponding data points on performance characteristic curves for the physical channel. From that mapping, an FER and a data rate can be selected to optimize system power allocation in respect to the data throughput requirement for the application and the characteristics of the selected channel.
In an alternative embodiment, channel conditions may be periodically sampled to model the performance characteristic curves in respect to temporal changes in the RF environment. The steps of the method of the invention are then iteratively repeated as the performance characteristic curves are updated, in order to dynamically control the system resource allocation under changing channel conditions.